Well after some calculations I came with the conclusion that it is possible with the following field:
F= r/(p^3) where r = <x,y,z> and p^3 = (x^2+y^2+z^2)^(3/2). The divergence is 0.
But does this exist on all of R^3?, since the denominator could be 0 at x,y,z=0?